Environmental exposure to arsenic and its metabolites is a significant health concern to US and world populations, playing a causative role in the etiology of human pathologies, including cancer. The long-term goal of the proposed study is designed to identify mechanisms of toxicity that are a result of environmental exposures to arsenicals. It is hypothesized that arsenical toxicity, in part, is mediated through its disruption of the normal epigenetic state of cells, and this hypothesis is based on reports in the extant literature as well as these preliminary studies. This premise will be tested using advanced epigenetic technologies to analyze models of arsenical exposure. These models range from in vitro models of arsenical-mediated malignant transformation of human uroepithelial cells to well-characterized, ethnically important human populations exposed to known levels of environmental arsenicals through drinking water. Through three specific aims the effects of arsenicals on epigenetic regulation from the level of the individual gene to the level of the entire genome will be tested. The aims are to: 1) Investigate the mechanisms and phenotypic consequences of epigenetic activation of Wnt5a gene that has been observed in an in vitro model of arsenical-induced malignant transformation. 2) Identify the decisive changes in the epigenomic landscape over the time course of arsenical induced malignant conversion of the immortalized human bladder cell UROtsa, and determine the stability of these changes after removal of this stressor. 3) Identify epigenetic targets of arsenic in human populations exposed to known levels of arsenic in their drinking water. While this research application focuses on the epigenetic perturbations induced by arsenicals with respect to human cancer, it is likely that if the hypothesis is backed by the studies, that of arsenical induced epigenetic changes as a mechanism of long-term toxicity, then the knowledge generated will likely extend to other metal-induced human pathologies, such as diabetes and cardiovascular disease.